Why is kswapd0 running on a computer with no swap?
I have a cloud server with ~14G of RAM and no swap. However, I occasionally see kswapd0 taking up some CPU when I run top. Why would kswapd0 be running at all if there's no swap space for it to manage?
swap
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
add a comment |
I have a cloud server with ~14G of RAM and no swap. However, I occasionally see kswapd0 taking up some CPU when I run top. Why would kswapd0 be running at all if there's no swap space for it to manage?
swap
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
add a comment |
I have a cloud server with ~14G of RAM and no swap. However, I occasionally see kswapd0 taking up some CPU when I run top. Why would kswapd0 be running at all if there's no swap space for it to manage?
swap
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
I have a cloud server with ~14G of RAM and no swap. However, I occasionally see kswapd0 taking up some CPU when I run top. Why would kswapd0 be running at all if there's no swap space for it to manage?
swap
swap
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
asked Mar 11 '14 at 16:33
Thomas JohnsonThomas Johnson
226149
226149
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
It still has a process to check if there's any swap. To reduce it, you'll need to set your swappiness -
edit "/etc/sysctl.conf" as root, then change (or add)
vm.swappiness = 0
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
ifkswapd0is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.
– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled andkswapd0is using some CPU and you do not want that, lower theswappinesssetting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering theswappinessreduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.
– Mikko Rantalainen
Feb 15 '18 at 13:15
add a comment |
Swap space is only used for data that is not backed by any other file. Data that is mapped from other files on disk ( such as executable programs ) is still swapped to their respective files even if you don't have a swap device.
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
add a comment |
If you have no swap and kswapd0 is running, your system is actually using nearly all of the RAM at that moment. It's time to get better tools to monitor memory usage (or free/available memory in the system).
The real fix is to reduce memory usage (run processes with less memory leaks, run less processes, skip running some processes at all, limit number of children/worker processes of some server software) or to get more RAM. If the need for RAM is caused by memory leaks, you may opt to use swap instead. Linux should be pretty smart getting the leaked parts to swap given enough time. Having swap is better than nothing but that is not a real substitute for having adequate amount of RAM.
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
add a comment |
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3 Answers
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active
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3 Answers
3
active
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It still has a process to check if there's any swap. To reduce it, you'll need to set your swappiness -
edit "/etc/sysctl.conf" as root, then change (or add)
vm.swappiness = 0
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
ifkswapd0is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.
– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled andkswapd0is using some CPU and you do not want that, lower theswappinesssetting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering theswappinessreduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.
– Mikko Rantalainen
Feb 15 '18 at 13:15
add a comment |
It still has a process to check if there's any swap. To reduce it, you'll need to set your swappiness -
edit "/etc/sysctl.conf" as root, then change (or add)
vm.swappiness = 0
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
ifkswapd0is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.
– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled andkswapd0is using some CPU and you do not want that, lower theswappinesssetting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering theswappinessreduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.
– Mikko Rantalainen
Feb 15 '18 at 13:15
add a comment |
It still has a process to check if there's any swap. To reduce it, you'll need to set your swappiness -
edit "/etc/sysctl.conf" as root, then change (or add)
vm.swappiness = 0
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
It still has a process to check if there's any swap. To reduce it, you'll need to set your swappiness -
edit "/etc/sysctl.conf" as root, then change (or add)
vm.swappiness = 0
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
answered Mar 11 '14 at 16:44
Elliott FrischElliott Frisch
2,17311117
2,17311117
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
ifkswapd0is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.
– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled andkswapd0is using some CPU and you do not want that, lower theswappinesssetting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering theswappinessreduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.
– Mikko Rantalainen
Feb 15 '18 at 13:15
add a comment |
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
ifkswapd0is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.
– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled andkswapd0is using some CPU and you do not want that, lower theswappinesssetting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering theswappinessreduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.
– Mikko Rantalainen
Feb 15 '18 at 13:15
3
3
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
Ok, but why is it using 1% of my cpu?
– portforwardpodcast
Jun 10 '15 at 23:00
if
kswapd0 is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.– Mikko Rantalainen
Feb 15 '18 at 13:12
if
kswapd0 is taking any CPU and you do not have swap, the system is nearly out of RAM and is trying to deal with the situation by (in practise) swapping pages from executables. The correct fix is to reduce workload, add swap or (preferably) install more RAM. Adding swap will improve performance because kernel will have more options about what to swap to disk. Without swap the kernel is practically forced to swap application code.– Mikko Rantalainen
Feb 15 '18 at 13:12
If you have swap enabled and
kswapd0 is using some CPU and you do not want that, lower the swappiness setting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering the swappiness reduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.– Mikko Rantalainen
Feb 15 '18 at 13:15
If you have swap enabled and
kswapd0 is using some CPU and you do not want that, lower the swappiness setting. However, unless your swap is backed by SSD that suffers from writing (e.g. bad wear leveling algorithm), lowering the swappiness reduces the system overall performance. The idea is to keep a copy of RAM in the swap in case more RAM is needed - in that case the copy in RAM is thrown away immediately instead of starting to swap that out before the RAM can be used. This optimistic swapping is only done while system is idle enough so it should never slow down your system.– Mikko Rantalainen
Feb 15 '18 at 13:15
add a comment |
Swap space is only used for data that is not backed by any other file. Data that is mapped from other files on disk ( such as executable programs ) is still swapped to their respective files even if you don't have a swap device.
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
add a comment |
Swap space is only used for data that is not backed by any other file. Data that is mapped from other files on disk ( such as executable programs ) is still swapped to their respective files even if you don't have a swap device.
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
add a comment |
Swap space is only used for data that is not backed by any other file. Data that is mapped from other files on disk ( such as executable programs ) is still swapped to their respective files even if you don't have a swap device.
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
Swap space is only used for data that is not backed by any other file. Data that is mapped from other files on disk ( such as executable programs ) is still swapped to their respective files even if you don't have a swap device.
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
answered Mar 11 '14 at 17:15
psusipsusi
31.2k15088
31.2k15088
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
add a comment |
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
3
3
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
For example, consider a case where you have zero swap and system is nearly running out of RAM. The kernel will take memory from e.g. Firefox (it can do this because Firefox is running executable code that has been loaded from disk - the code can be loaded from disk again if needed). If Firefox then needs to access that RAM again N seconds later, the CPU generates "hard fault" which forces Linux to free some RAM (e.g. take some RAM from another process), load the missing data from disk and then allow Firefox to continue as usual. This is pretty similar to normal swapping and kswapd0 does it.
– Mikko Rantalainen
Feb 15 '18 at 13:08
add a comment |
If you have no swap and kswapd0 is running, your system is actually using nearly all of the RAM at that moment. It's time to get better tools to monitor memory usage (or free/available memory in the system).
The real fix is to reduce memory usage (run processes with less memory leaks, run less processes, skip running some processes at all, limit number of children/worker processes of some server software) or to get more RAM. If the need for RAM is caused by memory leaks, you may opt to use swap instead. Linux should be pretty smart getting the leaked parts to swap given enough time. Having swap is better than nothing but that is not a real substitute for having adequate amount of RAM.
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
add a comment |
If you have no swap and kswapd0 is running, your system is actually using nearly all of the RAM at that moment. It's time to get better tools to monitor memory usage (or free/available memory in the system).
The real fix is to reduce memory usage (run processes with less memory leaks, run less processes, skip running some processes at all, limit number of children/worker processes of some server software) or to get more RAM. If the need for RAM is caused by memory leaks, you may opt to use swap instead. Linux should be pretty smart getting the leaked parts to swap given enough time. Having swap is better than nothing but that is not a real substitute for having adequate amount of RAM.
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
add a comment |
If you have no swap and kswapd0 is running, your system is actually using nearly all of the RAM at that moment. It's time to get better tools to monitor memory usage (or free/available memory in the system).
The real fix is to reduce memory usage (run processes with less memory leaks, run less processes, skip running some processes at all, limit number of children/worker processes of some server software) or to get more RAM. If the need for RAM is caused by memory leaks, you may opt to use swap instead. Linux should be pretty smart getting the leaked parts to swap given enough time. Having swap is better than nothing but that is not a real substitute for having adequate amount of RAM.
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
If you have no swap and kswapd0 is running, your system is actually using nearly all of the RAM at that moment. It's time to get better tools to monitor memory usage (or free/available memory in the system).
The real fix is to reduce memory usage (run processes with less memory leaks, run less processes, skip running some processes at all, limit number of children/worker processes of some server software) or to get more RAM. If the need for RAM is caused by memory leaks, you may opt to use swap instead. Linux should be pretty smart getting the leaked parts to swap given enough time. Having swap is better than nothing but that is not a real substitute for having adequate amount of RAM.
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
answered Jan 8 at 13:14
Mikko RantalainenMikko Rantalainen
574515
574515
add a comment |
add a comment |
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